JP2006010442A - Method for removing glass - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for removing glass which makes it possible to easily separate the glass for vitrifying a radioactive liquid waste adhering to a brick's surface from it. <P>SOLUTION: The direct irradiation of the brick's surface to which the glass adheres with laser light causes the thermal expansion of only the glass for vitrifying the radioactive liquid waste, and the glass is removed from the brick's surface by crashing the glass through its brittle fracture. The irradiation intensity, spot diameter and scanning speed of laser light is set so properly that thermal expansion distortion can be imparted especially to only the glass for vitrifying the radioactive liquid waste. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a glass removal method suitable for separating, for example, glass adhering to a brick surface constituting an inner wall surface of a glass melting furnace from the brick and disposing it as high-level radioactive waste.

Disposal of the high-level radioactive liquid waste that accompanies the reprocessing of the spent nuclear fuel, for example, after vitrifying the high-level radioactive liquid waste using borosilicate glass, the vitrified material is referred to as an overpack. It is carried out by being buried in the ground after being sealed and stored in a cylindrical carbon steel disposal container.
By the way, the lifetime of the glass melting furnace used for the vitrification treatment of the high-level radioactive liquid waste is relatively short. Therefore, it is necessary to disassemble and discard the glass melting furnace used for a certain period. At this time, since the glass adhering to the surface of the brick (refractory brick) that constitutes the inner wall surface of the glass melting furnace contains high-level radioactive material, it is disposed of after taking measures against radiation leakage in the same manner as the above-mentioned glass solidified body. It is necessary to do.

  Therefore, conventionally, a brick block body obtained by dismantling a glass melting furnace is attached to the surface of the brick 1 by irradiating laser light L parallel to the glass attachment surface of the brick 1 as shown in FIG. It is considered that the surface layer including the glass layer 2 is cut over a predetermined thickness (for example, about 15 mm) and only the surface layer including the glass layer 2 is disposed as radioactive waste separated from the brick 1. Yes.

As a technique for decontaminating the surface of inorganic materials such as concrete contaminated with radioactive materials, it is proposed to irradiate the surface of the inorganic material with laser light to vitrify or exfoliate the surface of the inorganic material. (See, for example, Patent Document 1). In addition, in order to remove contaminants such as a metal oxide film attached to the inner surface of a reactor vessel, a heat transfer tube, etc. in a nuclear reactor, it is also proposed to remove the contaminants by irradiating a laser beam (for example, Patent Document 2). , 3). Furthermore, it has also been proposed that the contaminated portion of the inorganic surface layer is irradiated with laser light to melt the contaminated portion, and the high-pressure gas is blown onto the molten layer to form the pollutant powder, and then the pollutant powder is recovered. (For example, refer to Patent Document 4).
JP 2000-346991 A JP 2001-59892 A JP-A-9-281296 JP 2001-116892 A

  However, as shown in FIG. 1, when the surface layer including the glass layer 2 is cut over a predetermined thickness by irradiating the laser beam L parallel to the glass adhesion surface of the brick 1, the glass having a thickness of about 1 to 2 mm. Since a considerable amount of bricks are cut out together with the layer 2, it cannot be denied that the amount of radioactive waste increases. And the disposal object is the brick 1 which the glass containing a high level radioactive substance adhered to the surface, and as shown in patent document 1 mentioned above, the surface is not an inorganic substance surface layer, such as concrete contaminated with the radioactive substance. Therefore, it is impossible to vitrify or peel off the surface layer of this inorganic substance. Moreover, since it is not contaminants, such as a metal oxide film adhering to the inner surface of metal objects, such as a furnace vessel, as shown in Patent Documents 2 and 3, the glass layer 2 adhering to the brick 1 is formed even when irradiated with laser light. It does not peel off like metal oxides.

  The present invention has been made in view of such circumstances, and its purpose is to separate the glass containing high-level radioactive material attached to the brick surface from the brick and dispose of the glass as high-level radioactive waste. It is another object of the present invention to provide a glass removal method suitable for this purpose.

In order to achieve the above-described object, the glass removal method according to the present invention is configured to irradiate laser light to the glass adhesion surface of the brick when separating the radioactive waste liquid solidified glass adhering to the surface of the brick. The glass is thermally expanded and crushed by brittle fracture of the glass, thereby being removed from the brick surface.
That is, in the present invention, the radioactive liquid waste solidified glass adhering to the surface of the brick is amorphous, its heat transfer coefficient is small, and when the glass is thermally expanded without melting, it is caused by the stress strain. We focus on the occurrence of brittle fracture. Therefore, in the present invention, by directly irradiating the radioactive waste liquid solidified glass adhering to the brick surface with laser light, the radioactive waste liquid solidified glass is subjected to thermal expansion distortion, and the solidified glass is crushed (crushed) by brittle fracture. It is characterized in that the radioactive waste liquid-solidified glass is removed from the surface of the brick by the occurrence.

  Preferably, as the laser beam, a YAG laser having a constant output (for example, about 0.5 kW) is used as the laser beam, and a distance between the laser processing head that outputs the YAG laser and the glass adhesion surface of the brick is set. While irradiating the glass adhering surface with laser light having a constant spot diameter by keeping it constant, the irradiation position is scanned over the entire area of the glass adhering surface, thereby solidifying radioactive waste liquid adhering to the brick surface. It is desirable to crush and separate the glass.

  When the brick constitutes an inner wall surface of a glass melting furnace for vitrifying high-level radioactive liquid waste as described in claim 3, for example, a manipulator supporting a laser processing head is installed in the glass melting furnace, It is desirable that the manipulator is remotely operated to sequentially crush the glass adhering surface of the brick constituting the inner wall surface of the glass melting furnace.

  According to the present invention, heat that does not melt the solidified glass is locally and suddenly applied only to the radioactive waste liquid solidified glass adhering to the brick surface, thereby generating thermal stress in the glass, thereby causing the solidified glass. Can cause brittle fracture to be crushed and separated from the above bricks, greatly increasing the amount of high-level radioactive waste compared to cutting and disposing of the brick surface layer including the glass layer. Can be reduced. In particular, by applying thermal energy only to the radioactive liquid waste solidified glass adhering to the brick surface by laser light irradiation, the radioactive liquid waste solidified glass is crushed by brittle fracture caused by the stress due to thermal expansion. The removal of the waste liquid solidified glass can be ensured.

  In addition, using a YAG laser, which is relatively easy to obtain a large output, while maintaining a constant distance between the laser processing head and the glass adhesion surface of the brick, the irradiation position of the laser beam with a constant spot diameter is set to the entire area of the glass adhesion surface. Since the radioactive liquid waste solidified glass at the laser light irradiation position can be crushed sequentially only by scanning over the surface, the radioactive liquid waste adhering to the surface from the entire inner wall surface of the glass melting furnace composed of bricks The solidified glass can be efficiently pulverized and removed, and the practical effects such as reduction of the amount of waste can be achieved.

  Hereinafter, with respect to the glass removal method according to an embodiment of the present invention with reference to the drawings, when disassembling a glass melting furnace used for vitrification treatment of high-level radioactive liquid waste generated along with reprocessing of spent nuclear fuel, The case where the radioactive waste liquid solidified glass adhering to the surface of the brick which comprises the inner wall face of the said glass melting furnace is removed from the said brick and it disposes as a high level radioactive waste is demonstrated to an example.

  The glass removing method according to the present invention basically uses a laser beam L directly on a glass adhering surface (radioactive waste liquid-solidified glass) on a brick 1 having a radioactive waste liquid-solidified glass 2 adhered to the surface as shown in FIG. The radioactive waste liquid solidified glass 2 is pulverized by irradiating the glass, and thereby only the radioactive waste liquid solidified glass 2 is removed from the brick 1. Specifically, for example, the laser light L is irradiated from the direction perpendicular to the glass adhesion surface toward the glass adhesion surface of the brick 1, and the irradiation position of the laser light L is set to the entire area of the glass adhesion surface of the brick 1. The glass layer 2 adhering to the surface of the brick 1 is sequentially crushed and removed by scanning over a distance.

  In particular, in order to heat only the solidified glass 2 while keeping the irradiation condition of the laser beam L on the glass adhering surface constant, the facing distance between the laser processing head 3 that irradiates the laser beam L with a constant output and the glass adhering surface of the brick 1 is set. By keeping constant, the irradiation spot diameter D of the laser light L is made constant, that is, the irradiation intensity of the laser light L is made constant. In this state, the entire surface of the glass adhesion surface is scanned while moving the irradiation position of the laser light L on the glass adhesion surface of the brick 1 at a constant speed. Specifically, a YAG laser beam with an output of 0.5 kW is used, for example, as shown in FIG. 3, while irradiating the glass adhering surface while keeping the irradiation spot diameter D of the laser beam L at 10 mm, the irradiation position is fixed to the left and right. Scan at speed. Further, the entire area of the glass adhering surface may be scanned by displacing the scanning line of the laser light L in a direction perpendicular to the scanning direction with a pitch width p of 6 mm.

  If the laser beam L is directly irradiated onto the glass adhesion surface of the brick 1 in this way, the radioactive waste liquid solidified glass 2 adhered to the surface of the brick 1 receives the light energy from the laser beam L and thermally expands. At this time, since the radioactive waste liquid solidified glass 2 itself is amorphous and its thermal conductivity is low, only the solidified glass 2 irradiated with the laser light L can be heated. In other words, the output (irradiation intensity) of the laser beam L is set in advance so that the brick 1 is not heated. Then, since only the solidified glass 2 having a thickness of about 1 to 2 mm attached to the surface of the brick 1 which is a large block body is heated by the irradiation of the laser light L and causes thermal expansion, between the brick 1 which does not thermally expand. Strain stress occurs. The solidified glass 2 is crushed by causing brittle fracture due to its thermal expansion, and is peeled off from the surface of the brick 1, and the crushed solidified glass 2 (crushed pieces or crushed powder) is separated from the surface of the brick 1.

  That is, if the solidified glass 2 is directly irradiated with the laser beam L, only the solidified glass 2 is locally heated thereby, and the solidified glass 2 is crushed by brittle fracture due to its thermal expansion. Separate from the surface. Therefore, by sequentially crushing the solidified glass 2 while scanning the irradiation position of the laser beam L, it is possible to remove the solidified glass 2 adhering to the surface of the brick 1 from the surface of the brick 1 while crushing. It becomes. Accordingly, only the solidified glass 2 attached to the surface of the brick 1 can be removed from the brick 1, so that the amount of high-level radioactive waste can be reduced. Specifically, it is only necessary to remove the solidified glass 2 attached to the surface of the brick 1 over a thickness of about 2 mm. Compared to the case where the surface of the brick 1 is cut to a thickness of about 15 mm with a laser beam. Thus, the amount of waste can be greatly reduced.

  The following table shows the thermal analysis of the irradiation energy amount (relative value) when the YAG laser beam L with an output of 0.5 kW is used and the scanning speed and spot diameter, which are the control parameters, are changed.

Based on the thermal analysis results, the present inventors extracted the irradiation conditions of the laser beam L that are likely to separate the glass 2 to some extent as shown as shaded areas in Table 1, and for each of these conditions The experiment gave the following results.
(1) When the spot diameter D is 1 mm, the solidified glass 2 does not melt and cause cracks.
(2) Even if the spot diameter D is set to 4 mm, the solidified glass 2 melts and cracks hardly occur.
(3) When the spot diameter D is 10 mm, the glass adhesion surface hardly changes when the scanning speed is high, but when the scanning speed is slow, the glass adhesion surface cracks. Further, the glass 2 does not melt.
(4) When the spot diameter D is set to 20 mm, the glass adhesion surface is cracked by further reducing the scanning speed.

  From this experimental result, it is considered that when the irradiation spot diameter of the laser beam L is reduced, the energy density of the irradiation region of the laser beam L is increased, thereby adding excessive heat energy and melting the solidified glass 2. In addition, when the irradiation spot diameter of the laser beam L is increased to some extent, this increases the energy density of the irradiation region of the laser beam L. However, if the scanning speed is fast, sufficient thermal energy is obtained to thermally expand the solidified glass 2. It is thought that cannot be granted.

  Therefore, from the above experimental results, for example, in order to remove the radioactive liquid waste solidified glass 2 having a thickness of about 1 to 2 mm from the surface of the brick 1, the irradiation spot diameter D of the laser beam L is preferably set to 10 mm, and the scanning speed thereof. Is set to 200 to 300 mm / min, the glass adhering surface is crushed to a thickness of about 1 to 2 mm and removed from the surface of the brick 1 without melting the solidified glass 2 adhering to the surface of the brick 1. We were able to confirm that

  4 (a) and 4 (b) show the state of the glass adhering surface of the brick 1 with radioactive waste liquid solidified glass 2 adhering to the surface (before irradiation with the laser beam L) and the above-mentioned conditions on the glass adhering surface of the brick 1 described above. It is the photograph which contrasts and shows the state after irradiating the laser beam L and grind | pulverizing the glass 2. FIG. As apparent from the comparison of these photographs, the ground of the brick 1 is exposed in the irradiation region of the laser beam L (see FIG. 4B), and the solidified glass 2 attached to the surface of the brick 1 is exposed. It can be understood that crushed and disappeared (removed).

  Therefore, when only the solidified glass 2 adhering to the surface of the brick 1 is crushed, the laser light L having such an intensity that the solidified glass 2 is not melted is used, and thermal expansion occurs efficiently within a certain range. If the irradiation spot diameter D of the laser beam L is set to, many cracks are generated in the solidified glass 2 and the glass 2 is crushed by brittle fracture. And it became clear that the solidified glass 2 adhering to the surface of the brick 1 can be efficiently removed by sequentially enlarging the crushing area | region of the solidified glass 2 mentioned above by the scanning of the laser beam L.

  In scanning the laser beam L, the scanning pitch p may be determined according to the width (size) of the crack. Further, in order to remove the adhered glass 2 from the surface of the brick 1 constituting the inner wall surface in the glass melting furnace, for example, a manipulator (not shown) provided in the glass melting furnace and supporting the laser processing head 3 is provided. The position where the laser processing head 3 faces the glass adhering surface of the brick 1 may be sequentially changed by remote control. Prior to dismantling the glass melting furnace in this way, if the radioactive waste liquid-solidified glass 2 is removed from the inner wall surface of the brick 1 that has constructed the glass melting furnace, the radioactive waste liquid-solidified glass 2 peeled off from the inner wall surface of the glass melting furnace is provided. Can be disposed of as high-level radioactive waste in advance, which facilitates the dismantling of the glass melting furnace. Moreover, about the removal operation | work of the glass 2 by irradiation of the laser beam L with respect to the glass adhesion surface, for example, the scanning may be repeatedly performed several times until the background of the brick 1 is exposed, and the radioactive waste removal is assured. Is preferred.

  In addition, the output of the laser beam L may be determined according to the thickness of the glass 2 attached to the surface of the brick 1 and can be implemented with various modifications without departing from the gist thereof. .

The conceptual diagram which shows the removal method of the glass adhering to the brick surface considered conventionally. The figure which shows the processing concept of the glass removal method which concerns on this invention. The figure which shows the scanning example of the irradiation position of the laser beam with respect to the glass adhesion surface of a brick. The photograph which contrasts the state of the glass adhesion surface of a brick, and the state of the surface of the brick which removed glass by irradiation of the laser beam.

Explanation of symbols

1 Bricks 2 Radioactive Waste Solidified Glass 3 Laser Processing Head L Laser Light

Claims (3)

When separating the radioactive liquid waste solidified glass adhering to the brick surface,
A glass removing method comprising irradiating a glass adhering surface of the brick with a laser beam to thermally expand the radioactive waste liquid-solidified glass and crushing and removing the glass by brittle fracture. The laser beam is a constant output YAG laser,
The distance between the laser processing head that outputs the YAG laser and the glass adhesion surface of the brick is kept constant, and the irradiation position of the glass adhesion surface is irradiated while irradiating the glass adhesion surface with laser light having a constant spot diameter. The glass removal method according to claim 1, wherein the radioactive waste liquid-solidified glass adhering to the surface of the brick is crushed and separated by scanning over the entire area. The brick constitutes the inner wall surface of a glass melting furnace that vitrifies high-level radioactive liquid waste,
2. A manipulator supporting a laser processing head is installed in the glass melting furnace, and the manipulator is remotely operated to crush the glass adhesion surface of a brick constituting the inner wall surface of the glass melting furnace. The glass removing method according to 1.